There is problem in Acid3 when Windows like smoothing is switched on (according to http://webkit.org/blog/168/gdi-text-on-windows/ ) in last nightly WebKit-r31238 in Windows XP. The shadow on Acid3 word is missing completelly. Note: on other sites text-shadow works, e.g. it works for headings on Webkit.org blog.
The latest nightly actually doesn't have shadows in it yet. It missed the checkin by *that* much. :) The next nightly will have it.
Ok, it's fixed in nightly r31308.